I want to make sure my backup are safe. I use one main SSD running Ubuntu and I have 2X 2Tb HDD in RAID1 for my data. How to know when a disk fail?
You could definitely check the disk SMART data.
If you use ubuntu desktop, run the
If you use a server, you can install smartmontools:
where you substitute "/dev/sdx" with your drive.
If you don't have a GUI, you can ask
That will list the Active, Working, Failed, and Spare devices for the array